When the CPython test suite re-runs a flaky failed test, it doesn’t actually re-run just that failed test but the entire test file. The most common case for flaky tests is when networking, threading, or multiprocessing is involved. Frustratingly those are some of the largest test files we have. Re-running them takes a lot of time.

Instead of re-running the entire file, regrtest should only re-run what actually failed.

NOTE: I added 3.10 and 3.9 to this issue even though it's not a pure bugfix. The reason is that this can visibly speed up CI for open pull requests.

(Of course, it would be best to avoid flaky tests altogether and we’re working on that, but re-running what failed is a pragmatic stopgap that is necessary in times of distributed CI that we don’t fully control.)

New changeset f1afef5e0d93d66fbf3c9aaeab8b3b8da9617583 by Łukasz Langa in branch 'main':
bpo-44708: Only re-run test methods that match names of previously failing test methods (GH-27287)
https://github.com/python/cpython/commit/f1afef5e0d93d66fbf3c9aaeab8b3b8da9617583

New changeset 9608719e12b14087c1cb34f77c847974442cd6e7 by Miss Islington (bot) in branch '3.10':
bpo-44708: Only re-run test methods that match names of previously failing test methods (GH-27287) (GH-27290)
https://github.com/python/cpython/commit/9608719e12b14087c1cb34f77c847974442cd6e7

New changeset 0f55d21212a0fb6dec4479eb76249ab2b54e57a3 by Łukasz Langa in branch '3.9':
[3.9] bpo-44708: Only re-run test methods that match names of previously failing test methods (GH-27287) (GH-27293)
https://github.com/python/cpython/commit/0f55d21212a0fb6dec4479eb76249ab2b54e57a3